1. Field of the Invention
The present invention relates generally to an ophthalmic refractor and more particularly to an ophthalmic refractor having an enhanced operability.
2. Related Background Arts
This kind of ophthalmic refractor includes a visual acuity chart presenting device such as a chart projector etc that has a plurality of charts containing symbols indicating different visual acuity values. The visual acuity chart presenting device is constructed to select the chart by inputting a visual acuity value of the symbols through ten keys, which should be shown to a patient.
In recent years, there has hitherto got prevailed an ophthalmic refractor including chart selection keys corresponding to the respective charts, and up- and down-keys for automatically inputting a visual acuity value and automatically selecting a chart in order to enhance the operability when examining a visual acuity of the patient.
In the case of selecting a chart containing Landolt rings indicating visual acuity values of, e.g., 0.4-0.6 by use of the chart selection key, an arbitrary visual acuity value of 0.4 among the values of 0.4-0.6 is displayed on a display unit. Then, the ophthalmic refractor is constructed so that when the displayed visual acuity value is sequentially incremented (such as 0.5, 0.6) by the up- and down-keys, the chart containing the symbol of the visual acuity value 0.7 is automatically presented to the patient even if the chart shown presently contains just the symbol indicating the visual acuity values of 0.6 and less.
Further, the ophthalmic refractor incorporates a function to mask the chart in order to make the patient visually recognize only a specific symbol in the chart presented. The mask is classified into a lengthwise one-column mask, a crosswise one-row mask and a one-character mask, which are movable in predetermined directions by using a mask operation key.
Note that the visual acuity value displayed on the display unit is stored as an ophthalmic result.
In the ophthalmic refractor having the above-described up- and down-keys and the mask operation key, the chart is masked so that the patient visually recognizes the symbol of the visual acuity value 0.4, and thereafter the visual acuity value is updated by the up- and down-keys. For example, when the visual acuity value is updated from 0.4 to 0.5, the updating process of the visual acuity value must be done by the up- and down-keys, and the mask has to be moved to a symbol by the mask operation key, which mark should be visually recognized by the patient. The operations of both of the up- and down-keys and the mask operation key on the occasion of the eye examination involving the use of the mask, might conduce to problems in which an eye examining time increases, and besides the operation becomes troublesome. Further, it might happen that the operation by the up- and down-keys gets misconceived as the operation by the mask operation key, which leads to a possibility in which the updated visual acuity value is not coincident with the symbol that should be visually recognized by the patient.
Furthermore, according to the ophthalmic refractor including the up- and down-keys for the visual acuity values, the operation of the up- and down-keys is invariably interlocked with the visual acuity chart operating device, and hence only the chart can not be arbitrarily selected without updating the visual acuity value.
Further, if the visual acuity values of the symbols contained in the charts are limited to 0.1, a displayable visual acuity value is also limited to 0.1, and it is impossible to perform the eye examination for visual acuity values smaller than 0.1.